1. Field of the Invention
This invention relates to speakers and, in particular, to speakers having a dome-shaped diaphragm.
2. Discussion of the Prior Art
In most conventional dome type speakers, the dome has a diameter not greater than 60 mm. Such speakers usually include a circular-shaped voice coil mounted on an outer peripheral portion of a circular dome type diaphragm. As a consequence, conventional dome type speakers suffer from various drawbacks as noted below:
A. A satisfactory oscillation area for improving directivity cannot be obtained. In addition, when the Q of the low-pass resonance region of the oscillation system is designed to provide a uniform regeneration band to cover the low-pass region, efficiency is decreased, and if it is designed to increase efficiency, the Q decreases in value, resulting in a narrow regeneration band. PA1 B. Generally stated, in dome type speakers, the voice coil functions to drive the outer peripheral portion of the dome-shaped diaphragm, and for this reason, transfer of high-pass components in the diaphragm, in a split band, occurs in a closed path at top of the diaphragm to generate a standing wave in the diaphragm to decrease energy loss therein. This causes a deviation in phase between the top of the diaphragm and the outer peripheral portion by the voice coil to produce "peak-dip" or dip in the frequency characteristic. In order to improve this, an equalizer may be used; however, the use thereof provides no essential improvement in the poor movement of the diaphragm. PA1 C. If loss in the diaphragm is increased, energy is not sufficiently transmitted to the top of the diaphragm, and although the peak-dip of the frequency characteristic may be improved, the efficiency in the high-pass region is decreased. Thus, there is a merit in the operational principle of a piston motion, but there is a significant disadvantage in terms of the physical characteristic in a split oscillation band. PA1 D. If a diaphragm of larger diameter is used to increase the efficiency, the upper limit of the high-pass region of the regeneration bandwidth is lowered, and if a further attempt is made, in order to improve the aforementioned drawback, to provide a sharp angle at the junction formed between the coil bobbin and the diaphragm, the equivalent mass of the diaphragm, particularly in the high-pass region, is increased, thereby resulting in a shortage of energy in this region.